Neurite outgrowth inhibitor of gliotic brain tissue. Mode of action and cellular localization, studied with specific monoclonal antibodies

Membranes from injured adult rat brain express a heparan/chondroitin sulphate proteoglycan that inhibits neurite outgrowth in vitro. We have developed monoclonal antibodies (Mabs) against this proteoglycan, two of which were characterized and used for the study of the inhibitor mode of action and localization in normal and injured adult brain. The antibodies recognized a molecule of apparent molecular weight 200 kDa in Western blots of injured brain membranes. One of the Mabs blocked both the inhibition of neurite outgrowth and the growth cone collapse activity, associated with the proteoglycan. In adult brain, inhibitor immunoreactivity was found predominantly in neurons but, after a lesion, it was associated mainly with reactive glial cells. The localization of neurite outgrowth inhibitors in reactive glia supports the idea that gliotic tissue is largely responsible for the failure of axonal regeneration in mammalian CNS.

Developmental distribution of glycosaminoglycans in embryonic rat brain: relationship to axonal tract formation

Glycosaminoglycans, the sugar moieties of proteoglycans, modulate axonal growth in vitro. However, their anatomical distribution in relation to developing axonal tracts in the rat brain has not been studied. Here, we examined the immunohistochemical distribution of chondroitin-6-sulfate and chondroitin-4-sulfate, two related glycosaminoglycan epitopes, which are present in three types of glycosaminoglycans: chondroitin sulfate C, chondroitin sulfate A, and chondroitin sulfate B. Further, we compared their distribution pattern to that of axonal tract development. Both glycosaminoglycan epitopes showed a heterogeneous spatiotemporal distribution within the developing rat brain. However, the expression of chondroitin-4-sulfate was more restricted than that of chondroitin-6-sulfate, although both epitopes were detected from embryonic day 13 until the day of birth, overlapping in many regions of the central nervous system including cortex, hippocampus, thalamus, and hindbrain. After birth, the levels of expression of both glycosaminoglycan epitopes progressively decreased and were practically undetectable after the first postnatal week. The expression of chondroitin-6-sulfate and, to a lesser extent, that of chondroitin-4-sulfate, was preferentially associated to the extracellular matrix surrounding specific axon bundles. However, the converse association was not true, and several apparently similar types of axon developed on a substrate devoid of both types of glycosaminoglycan epitopes. These results provide an anatomical background for the idea that different types of glycosaminoglycans may contribute to establish the complex set of guidance cues necessary for the specific development of defined axon tracts in the central nervous system.

Experimental brain glioma: growth arrest and destruction by a blood-group-related tetrasaccharide

A synthetic tetrasaccharide (TS4), structurally related to blood groups, inhibited the proliferation of the C6 glioma cells in culture and the growth of tumors formed after intracerebral transplantation of C6 cells. TS4-treated tumors were substantially smaller than controls, as expected from TS4 cytostatic action on C6 glioma cells in culture. However, in vivo treatment also caused extensive tumor destruction. This effect appeared to be caused by indirectly, either by activation of natural killer cells, cytotoxic lymphocytes, or by inhibition of tumor vascularization. Enhanced antigenicity of TS4-treated glioma may be related to the increased expression of connexin 43 observed in glioma cell cultures treated with the oligosaccharide. Because concentrations of up to 20 mg/ml of TS4 were not toxic for normal neuronal or glial cells, specific oligosaccharides such as TS4 offer the possibility of selective tumor treatment.

Chemical heterogeneity in adult rat cerebellar Purkinje cells as revealed by zebrin I and low-affinity nerve growth factor receptor immunocytochemical expression following injury

Cerebellar Purkinje cells in rat express low-affinity nerve growth factor receptor during development, but rarely in normal adult animals. However, after either mechanical injury or colchicine treatment during adulthood, these cells re-express low-affinity nerve growth factor receptor-immunoreactive protein. Two Purkinje cell subpopulations were defined in normal adult cerebellum by the presence or the absence of zebrin I antigen. Nevertheless, it remains an open question as to whether low-affinity nerve growth factor receptor-immunoreactive protein can be expressed by all damaged Purkinje cells, independent of their location and their staining with antibodies against intrinsic molecular markers that reveal Purkinje cell heterogeneity, such as zebrin I. In this study, a serial-section immunocytochemical mapping of the expression zebrin I and low-affinity nerve growth factor receptor, using specific monoclonal antibodies, we carried out in colchicine-treated rats. After mechanical damage of the cerebellar cortex, co-localization of these antigens at the cellular level was also analysed in thin adjacent sections, and by using a combined immunocytochemical staining method in individual sections. The findings revealed the existence of three sub-sets of Purkinje cells: (1) two complementary groups distinctly immunoreactive to one antibody, but not to the other and (2) a third group that contained double-labelled cells. In contrast, co-expression of both antigens was never observed following mechanical lesions. The seemingly independent response to mechanical injury of Purkinje cells located in different zebrin-defined compartments, indicates that particular subpopulations of Purkinje cells may respond differentially to traumatic injury.

Preparation of a monoclonal antibody to a glycidic epitope of the epidermal growth factor receptor that recognizes inhibitors of astrocyte proliferation and reactive microglia

A mouse monoclonal antibody (5B9), directed against a carbohydrate epitope of human epidermal growth factor receptor (EGFR), recognized an 81-kDalton glycoprotein in buffer-soluble and detergent-solubilized rat brain extracts (BE). The glycoprotein was more abundant in extracts prepared from injured brain than in those from normal tissue. Removal from BE of the antigens recognized by 5B9 increased their astrocyte mitogenic activity. Sections of injured rat brain and cultures derived from damaged brain, enriched in microglia, showed 5B9 immunoreactivity in ED1-positive cells. The abundance of the glycoprotein recognized by 5B9 in injured, relative to normal, tissue, suggested that molecules with EGFR immunoreactivity may be expressed in reactive microglial cells and released after injury.

Regeneration into the spinal cord of transected dorsal root axons is promoted by ensheathing glia transplants

The permissivity of adult olfactory bulb to the ingrowth of olfactory axons could be due to the unique properties of ensheathing glia. To test whether these glial cells could be used to promote axonal regeneration in a spontaneously nonregenerating system, we transplanted suspensions of pure ensheathing cells into a rhizotomized spinal cord segment. Ensheathing cells were purified away from other cell types by immunoaffinity, using anti-p75 nerve growth factor receptor. After laminectomy at the lower thoracic level, the spinal cord was exposed and one dorsal root (T10) was completely transected at the cord entry point. The root stump was microsurgically anastomosed to the cord and a suspension of ensheathing cells was transplanted in the spinal cord at the dorsal root entry zone. Three weeks after transplantation, numerous regenerating dorsal root axons were observed reentering the spinal cord. Ingrowth of dorsal root axons was observed using DiI and antibodies against calcitonin gene-related peptide and growth-associated protein. Primary sensory afferents invaded laminae 1, 2, and 3, grew through laminae 4 and 5, and reached the dorsal grey commissure and lamina 4 of the contralateral side. We did not observe regenerating axons within the ipsilateral ventral horn and dorsal column. Transplanted ensheathing cells reached the same laminae as axons. Neither ensheathing cells nor regenerating axons invaded those laminae they did not innervate under normal circumstances. In conclusion, the regeneration of injured dorsal root axons into the adult spinal cord was possible after ensheathing glia transplantation. The use of ensheathing cells as stimulators of axonal growth might be generalized to other central nervous system injuries.

Differential effects of glycosaminoglycans on neurite outgrowth from hippocampal and thalamic neurones

Chondroitin sulphate proteoglycans are expressed in a temporally restricted pattern from embryonic day 17 to postnatal day 0 in both the thalamus and the cortical subplate, to which thalamic neurones transiently project. To study whether chondroitin sulphate proteoglycans could be specifically involved in the modulation of thalamic axon outgrowth, we compared neurite outgrowth from cultured rat embryonic hippocampal and thalamic neurones, in the presence of chondroitin sulphate type C (isolated from shark cartilage) and chondroitin sulphate type B (dermatan sulphate; isolated from bovine mucosa). When added to the culture medium, both types of glycosaminoglycan lowered the adhesion to laminin and polylysine of both hippocampal and thalamic neurones. However, only chondroitin sulphate specifically modified the pattern of thalamic but not hippocampal neurone outgrowth, promoting axon growth. The morphological changes induced by chondroitin sulphate were concentration dependent and correlated with the selective binding of chondroitin sulphate to the neuronal plasma membrane and its subsequent internalisation. Chondroitin sulphate loosely bound to the surface of hippocampal neurones, but was not internalised. These results indicate that proteoglycans, and in particular the glycosaminoglycan component of these molecules, can differentially modulate neurite outgrowth, depending on their biochemical composition and on the type of neurones they bind to; this would be a possible mechanism of controlling axon guidance in vivo.

Active microglia, sick astroglia and Alzheimer type dementias

We propose that Alzheimer's disease is initiated by failure of axonal transport. After the neurodegeneration cascade is initiated, microglial and astroglial cells have major roles in directly and indirectly promoting self-sustaining neurodegeneration cycles. This hypothesis makes testable predictions and suggests logical therapies.

Neurite outgrowth inhibitors associated with glial cells and glial cell lines

'Reactive' astrocytes and 'activated' microglial cells are the major cellular components of gliotic tissue, one of the most serious obstacles to axonal regeneration in mammalian central nervous system grey and white matter. The appearance of reactive glial cells after a lesion in the CNS correlates with the expression of molecules, like proteoglycans, capable of preventing neurite outgrowth. Co-cultures of embryonic neurones with glial cells and glial cell lines, that might share characteristics with reactive astrocytes and microglial cells, show that while cultured astrocytes promote neurite outgrowth, plasma membranes of C6 glioma and microglial cells express neurite inhibitory activities with proteoglycan-like characteristics, similar to those expressed by the gliotic tissue associated inhibitors. These results suggest that in vivo microglial cells might be at least one of the sources of proteoglycans with neurite outgrowth inhibitory properties.

In vitro enfolding of olfactory neurites by p75 NGF receptor positive ensheathing cells from adult rat olfactory bulb

Secondary cultures of adult rat olfactory bulb (OB) contained three different types of cell: (i) process-bearing cells; (ii) macrophage-like cells and (iii) fusiform cells. The immunohistochemical properties of process-bearing cells closely corresponded to those described for ensheathing glia in vivo. The most distinctive feature of these cells was their immunoreactivity for low affinity nerve growth factor receptor (NGFR). Process-bearing cells also shared the ultrastructural properties of ensheathing glia in vivo, as well as the ability to ensheath olfactory axons. In contrast, macrophage-like cells had the immunostaining properties of microglia, and fusiform cells were likely capillary endothelial cells. Neurites outgrowing from olfactory epithelium explants, when co-cultured with adult OB cells, grew preferentially over NGFR positive cells. Olfactory neurites exhibited NGFR immunoreactivity and were enfolded by NGFR positive cells. After ensheathment, this immunoreactivity decreased from the neurite and disappeared from the glial membrane in contact with the neurite. However, NGFR immunoreactivity was maintained in the portion of the glial membrane not involved in ensheathing. In summary, ensheathing cells in vitro retained both the ultrastructure shown in vivo and the ability to ensheath olfactory neurites. The Schwann cell-like properties of ensheathing glia, could partially explain the permissibility of adult OB to axonal growth.

Differential activation of microglia and astrocytes in aniso- and isomorphic gliotic tissue

Reactive astrocytes and microglial cells are both involved in the formation of gliotic tissue. Using immunohistochemical markers, we have compared the response of both these cell types after two different kinds of damage in the brain: traumatic injury (anisomorphic gliosis) and neurotoxic induced lesion (isomorphic gliosis), in two distinct regions of the brain, the cortex and the hippocampus. We show that the time course and the relative contribution of astrocytes and microglial cells differ greatly in the two kinds of lesions. While in anisomorphic gliosis there is little activation of endogenous microglial cells independently of the brain region damaged, these cells contribute in large measure and for prolonged periods of time to the formation of isomorphic gliotic tissue. Astrocytes are quickly activated at the border of anisomorphic lesions, and after 3 days they already occupy an extensive portion of the brain parenchyma. However, after 1 month, they are found restricted to a thin strip at the lesion boundary. In contrast, after an isomorphic lesion, astrocytes become reactive around the site of neuronal cell loss but not at the site of the lesion itself. Only after 2 weeks do they totally invade the damaged region, persisting for at least 1 month. Such differences are observed independently of the brain region damaged. These results suggest that the cellular, and therefore the molecular, composition of gliotic tissue depends on the type of insult the CNS has suffered.

Differences between reactive astrocytes and cultured astrocytes treated with di-butyryl-cyclic AMP

The long-standing idea that astrogliosis acts as a barrier for regenerating axons could be tested if an in vitro model of reactive astrocytes were available. The morphology and intermediate filament content of cultured perinatal astrocytes treated with di-butyryl-cyclic-AMP are reminiscent of reactive astrocytes evoked by injury. Thus, they have been proposed as a reactive astrocyte in vitro model. However, we show here that di-butyryl-cyclic-AMP-treated astrocytes are much closer to untreated neonatal cells than to reactive astrocytes in vivo, when using other immunohistochemical markers of living reactive glia (i.e. EGF receptor or laminin). Furthermore, living di-butyryl-cyclic-AMP-treated astrocytes and untreated, flat, epithelioid cells, as well as their purified plasma membranes, had similar neurite outgrowth promoting properties, whereas membranes from gliotic tissue enriched in reactive astrocytes inhibited neurite outgrowth. Our observations indicate that di-butyryl-cyclic-AMP treatment leads, at best, to a morphological model of reactive cells that does not share many properties of reactive astrocytes in vivo.

Characterization of a neurite outgrowth inhibitor expressed after CNS injury

Reactive gliosis, a general response to injury in the central system grey and white matter, represents a serious obstacle to axonal regeneration in mammals. In culture, myelin-free plasma membranes from normal rat brain tissue promoted neurite outgrowth, whereas myelin-free membranes purified from injured tissue were inhibitory. The inhibitory activity could be solubilized by detergent, was sensible to glycosaminoglycan lyase digestion and eluted with an apparent molecular weight of 160-220 kDa in gel filtration chromatography. When presented as a surface-bound molecule, the inhibitor prevented neurite initiation; when added in a soluble form to growing neurites, it induced their retraction. These results provide cellular and molecular evidence supporting the classical view that, in the mammalian central nervous system, damage-evoked gliosis correlates with the expression of molecules capable of preventing neurite outgrowth.

Polymorphonuclear leukocytes in brain parenchyma after injury and their interaction with purified astrocytes in culture

At a time after brain injury when removal of debris and secondary cell death were prevalent, many polymorphonuclear neutrophils were observed in injured tissue. Because neural damage could be mediated by activated neutrophils, we tested in vitro the effect of these leukocytes and other blood components on central nervous system cells. At concentrations similar to those present in blood, polymorphonuclear leukocytes resulted in astrocyte detachment from the substrate and aggregation. These neutrophil concentrations affected both epithelioid and stellate HNK1/A2B5-negative (type 1) astrocytes but not hippocampal neurons. Substrate detachment was partially prevented by corticosterone, but not by protease inhibitors or free-radical scavengers. Co-cultures of purified cortical astrocytes with neutrophils (1/20 cell ratio) contained at the beginning of the experiment approximately 93-98% astrocytes with type 1 markers. After 6-8 days co-culture, many stellate cells insensitive to neutrophils seemed to migrate out of the aggregates. About 70% of these resistant cells had immunological markers typical of type 2 astrocytes. The possible relevance of these findings to reactive astrogliosis and secondary neuronal death is discussed.

Lesion-induced expression of low-affinity nerve growth factor receptor-immunoreactive protein in Purkinje cells of the adult rat

Normal adult cerebellar Purkinje cells in the rat rarely express low-affinity nerve growth factor receptor immunoreactivity. However, intense anti-low-affinity nerve growth factor receptor immunostaining was observed as early as one day after a lesion of the cerebellar cortex. Low-affinity nerve growth factor receptor immunoreactivity was confined to a selected group of Purkinje cells, the number of which reached a maximum at three days postlesion, and, in some neurons, persisted up to 10 days after damage. The intensity of Purkinje cell immunolabeling decayed abruptly with distance from the lesion site. Reactive Purkinje cells exhibited deposition of immunoreaction product in the cell soma, dendrites and axons. Characteristically, most Purkinje cell axons exhibiting intense low-affinity nerve growth factor receptor immunoreactivity had beaded, varicose morphology. Varicose fibres with the appearance of recurrent collaterals of Purkinje cell axons were also low-affinity nerve growth factor receptor-positive. Our results indicate that adult rat Purkinje cells increase low-affinity nerve growth factor receptor-immunoreactive protein in response to injury, suggesting that, in the cerebellum, low-affinity nerve growth factor receptor or low-affinity nerve growth factor receptor-like molecules may be involved in regulating neuronal plasticity during adulthood.

Inhibition of proliferation of normal and transformed neural cells by blood group-related oligosaccharides

A synthetic tetrasaccharide structurally related to blood groups and selectin ligands inhibited division of astrocytes, gliomas, and neuroblastomas at micromolar concentrations. The compound was cytostatic for primary astrocytes in culture, but cytotoxic for fast proliferating cell lines.

Glial cells from adult rat olfactory bulb: immunocytochemical properties of pure cultures of ensheathing cells

Three morphologically and immunohistochemically distinct types of cell were present in primary cultures of adult rat olfactory nerve and glomerular layers of the olfactory bulb. One cell type was multipolar and stained positively for glial fibrillary acidic protein; a second type had fried egg-like morphology and stained with antibodies to epitope ED1; the third cell type had fusiform morphology, reacted with antibodies to vimentin and laminin and was glial fibrillary acidic protein- and ED1-negative. Trypsinization of these primary cultures (3 min, 37 degrees C), detached multipolar and fusiform cells only. When detached cells were set up in secondary culture on a glass substrate, fusiform cells did not attach, resulting in a pure culture of multipolar cells. Multipolar cells were glial fibrillary acidic protein- and myelin basic protein-positive and had the properties of so-called ensheathing cells or Blanes' glia. Immunoreactivity with anti-nerve growth factor receptor and anti-fibronectin allowed us to identify four distinct populations of multipolar ensheathing cells. One population was nerve growth factor receptor-positive, fibronectin-negative. A second was nerve growth factor receptor-negative and fibronectin-positive. A third was positive for both markers and the remaining cells did not stain for either of them. The morphological and immunological characteristics of cultured cells from olfactory nerve and glomerular layers were similar to those of Schwann cells and the similarities could account for the permissivity to axonal growth of the olfactory bulb.

Sex differences in the effect of MK-801 on normal and spinal cord injured rats

The induction of functional paraplegia in female rats by contusive spinal cord injury was not prevented by compound MK-801. However, the treatment reduced cavitation around the lesion epicenter to 14 mm3 compared to 17 mm3 in untreated controls t-test, P < 0.28) and conserved more neurons in defined regions outside the lesion epicenter (drug-treated animals vs untreated controls: 299 vs 73 neurons/mm2; t-test, P < 0.009). Thus, although MK-801 was only partially effective in preventing neuronal death secondary to contusion injury it appeared to have a definite neuroprotective effect. In view of the variety of side effects of MK-801 and the controversy on the mechanism of neuroprotection, we examined the action of the drug on non-injured animals. The effects of the drug were strongly sex-dependent. One hour after subcutaneous injection (0.5 mg/kg), female rats were hypothermic (36.8 °C treated vs 38.3 °C control) whereas male rats were hyperthermic (39.6 °C treated vs 38.4 °C control). In females, MK-801 caused cessation of cycling and appearance of numerous polymorphonuclear (PMN) phagocytes in vaginal frotis. Also, beginning 24 h after MK-801 injection, the proportion of PMN increased 400% in female blood, whereas males maintained control values. Arthritis-like joint inflammation was prominent in the toes of female rats, but males were unaffected. After continued treatment with the drug for 15 days, PMN count in female rats decreased and the animals resumed cycling. However, during this period female rats lost 20% of their weight, whereas males gained 26%. One hour after MK-801 injection large increases in blood pressure occurred in both sexes, returning to normal values 2 h later. Hypothermia does not appear to be a factor in the neuroprotective effect of MK-801, but the drug has a number of potentially dangerous side effects, particularly in female rats. Because polymorphonuclear cells are known sources of oxygen free radicals, neuroprotection by MK-801 treatment ought to be much more efficient in males than in females and the drug should be used in combination with a free-radical scavenger.

Subcellular localization of nerve growth factor receptors in identified cells of the rat nucleus basalis magnocellularis: an immunocytochemical study

The subcellular location of nerve growth factor receptor in the ventromedial portion of rat globus pallidus was investigated with affinity-purified monoclonal 192-IgG following the unlabelled antibody peroxidase-antiperoxidase immunocytochemical procedure. At the light microscopic level, punctate immunoreaction product was observed in the perinuclear region and in the plasma membrane of large, probably cholinergic neurons. Examination in the electron microscope of these neurons confirmed that nerve growth factor receptor-stained cells were basal forebrain cholinergic neurons. Within these cells, immunostaining occurred in the Golgi apparatus, in multivesicular bodies and, occasionally, in rough endoplasmic reticulum cisternae and the nuclear envelope. Moreover, patches of immunoreactivity were observed associated with the outer surface of the plasma membrane of the soma and their proximal dendrites and also with the plasma membrane of distal dendrites showing scarcity of synaptic input. Positive immunostaining was never observed in synaptic clefts, but filled the space between the plasma membranes of immunoreactive neurons and those of thin glial processes in their vicinity. The location of membrane nerve growth factor receptor in close apposition to membranes of neighbouring astrocytes rather than near synaptic complexes, suggests that glial cells may be a physiological source of nerve growth factor.

Growth factors and growth factor receptors in the hippocampus. Role in plasticity and response to injury

Various growth factors are present in the hippocampal formation and appear responsible for the prominent plasticity of this brain area. Although hormone-like growth-promoting polypeptides are the best known, recent studies emphasize the importance in the growth response of molecules such as laminin proteoglycans, neurotransmitters and growth inhibitors. The progress and problems in the study of these substances are reviewed.

NGF receptor increase in the olfactory bulb of the rat after early odor deprivation

In the olfactory bulb of normal rats, nerve growth factor (NGF) receptor (NGFR) immunoreactivity was largely confined to the glomerular layer. Unilateral closure of the nostril at postnatal day 2 (P2) increased NGFR immunoreactivity in the sealed bulb at both 19 and 60 days after the operation. The increase in NGFR density, measured by autoradiographic immunohistochemistry, was most dramatic 60 days postocclusion. These findings suggest that a compensatory increase in NGFRs may play a role in the maintenance of bulbar function after the early loss of sensory stimulation.

Neuroprotective effect of MK-801 and U-50488H after contusive spinal cord injury

One hour before a contusive spinal cord injury either compound MK-801 or compound U-50488H was injected intraperitoneally, and a 14-day-delivery osmotic minipump containing the same drug was placed subcutaneously at the time of surgery. The motor and sensory behavior of the animals was measured over the following 30 days. Both MK-801 and U-50488H treatments had a statistically significant neuroprotective effect. The number of neurons per unit area outside the lesion epicenter was significantly (P less than 0.01) greater in the drug-treated animals (MK-801, 298.9 +/- 74.8 neurons/mm2; U-50488H, 242.7 +/- 16.5 neurons/mm2) than in untreated controls (73.3 +/- 9.3 neurons/mm2). Recovery of sensory and motor behavior was limited but significant differences were observed when drug-treated rats were compared with untreated controls. The effects of the two drugs were not additive for any of the variables studied.